Some of the island asks nothing of you but the walk. The historic sights cluster in and above Charlotte Amalie. That makes them the cheapest half-day outing on this list, and the easiest to fit around a fixed departure.
Visit USVI describes the 99 Steps as an 18th-century step-street, built from stone bricks brought here aboard Danish tall ships. It counts 103 steps rather than 99. The climb ends at Blackbeard’s Castle, a 1679 lookout tower built by Danish settlers. Fort Christian, down at the waterfront, was completed in 1680 and is the oldest structure still standing in the territory.
The rest is a matter of which view you want and how you reach it. Skyline Drive is the scenic road version, with Charlotte Amalie, Hassel Island and Water Island laid out below. The Skyride lifts you 700 feet instead. Drake’s Seat looks the other way, over the north side. A walk through Charlotte Amalie reaches most of the historic sights on foot.